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**15CrMo Boiler Tube Overview**
The **15CrMo boiler tube** is a type of high-quality carbon structural steel that incorporates one or more alloying elements to enhance its mechanical properties, toughness, and hardenability. These tubes are typically subjected to heat treatment processes such as normalization or quenching and tempering. Components made from this material often require additional treatments like quenching and tempering, surface chemical treatments (such as carburizing or nitriding), or even surface hardening techniques like induction or high-frequency quenching.
Based on its chemical composition—primarily the carbon content—and its intended use, 15CrMo steel can be broadly classified into three main categories: carburizing steels, quenching and tempering steels, and nitriding steels. Each category is designed for specific applications where strength, durability, and thermal resistance are critical.
**Classification of High-Pressure Boiler Tubes**
1. **High-quality carbon structural steel grades**: Includes 20G, 20MnG, and 25MnG.
2. **Alloy structural steel grades**: Such as 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB, etc.
3. **Rust and heat-resistant steels**: Commonly used grades include 1Cr18Ni9 and 1Cr18Ni11Nb. These materials must undergo hydrostatic, flaring, and flattening tests in addition to meeting chemical and mechanical requirements. They are delivered in a heat-treated condition.
In addition to these criteria, there are strict requirements regarding the microstructure, grain size, and decarburization layer of the finished steel pipe.
**Specifications and Appearance Quality**
According to GB5310-95 "Seamless Steel Tubes for High-Pressure Boilers," the outer diameter ranges from 22 to 530 mm, with wall thicknesses between 20 and 70 mm. Cold-drawn or cold-rolled tubes have smaller dimensions, with an outer diameter of 10–108 mm and wall thickness of 2.0–13.0 mm.
**Hydrogen Purification Principle Using 15CrMo Boiler Tubes**
At temperatures between 300–500°C, hydrogen gas passes through one side of the 15CrMo boiler tube. The hydrogen is adsorbed onto the inner surface due to the incomplete 4d electron shell of palladium, which allows it to form unstable bonds with hydrogen. This reaction is reversible. Under the influence of palladium, hydrogen is ionized into protons with a radius of approximately 1.5 × 10â»Â¹âµ m. Since the lattice constant of palladium is 3.88 × 10â»Â¹â° m at 20°C, these protons can recombine with electrons through the tube to form pure hydrogen molecules, which then exit the other side. Gaseous hydrogen that does not dissociate remains impermeable, allowing the 15CrMo tube to produce high-purity hydrogen.
**Representation of 15CrMo Boiler Tube Grades**
1. The first two digits in the steel grade indicate the average carbon content, expressed in ten-thousandths. For example, 40Cr indicates a carbon content of 0.40%.
2. Main alloying elements are usually denoted by their symbols. If the average alloy content is less than 1.5%, only the symbol is shown, but not the percentage. However, if confusion may arise, a "1" may be added after the symbol, such as in "12CrMoV" and "12Cr1MoV."
3. Microalloying elements like vanadium (V), titanium (Ti), aluminum (Al), boron (B), and rare earths (RE) are also marked in the grade, even in small amounts.
4. To distinguish high-quality steel from general-grade steel, "A" is added at the end of the grade.
5. Special-purpose alloys may include a symbol indicating their application, such as ML30CrMnSi for screw-making.
**Difference Between Alloy Pipes and Seamless Pipes**
While both alloy pipes and seamless pipes are types of steel tubes, they differ in classification. Alloy pipes are defined by their material composition, meaning they are made from alloy steel. Seamless pipes, on the other hand, refer to the manufacturing process, where the pipe has no weld seam. This is different from welded pipes, which include straight-seam and spiral-seam types.
**Weight Calculation Formula for 15CrMo Boiler Tubes**
To calculate the weight per meter of a 15CrMo boiler tube:
$$
\text{Weight (kg/m)} = [(Outer Diameter - Wall Thickness) \times Wall Thickness] \times 0.02466
$$
This formula provides a quick and accurate way to estimate the weight of the tube based on its dimensions.